1. Field of the Invention
The present invention relates to a method for manufacturing a package, a method for manufacturing a piezoelectric vibrator, a piezoelectric vibrator manufactured by the manufacturing method, and an oscillator, an electronic device, and a radio-controlled timepiece each having the piezoelectric vibrator.
2. Description of the Related Art
Recently, a piezoelectric vibrator utilizing quartz or the like is used in a cellular phone and a portable information terminal as the time source, the timing source of a control signal, a reference signal source, and the like.
As the piezoelectric vibrator of this type, an SMD (Surface Mount Device)-type piezoelectric vibrator as disclosed in JP-A-6-283951, for example, is known. As shown in FIGS. 21 and 22, a piezoelectric vibrator 200 includes a base board 201 and a lid board 202 which are bonded to each other, and a piezoelectric vibrating reed 203 which is sealed in a cavity C formed between both boards 201 and 202.
The piezoelectric vibrating reed 203 is, for example, a tuning-fork type vibrating reed and is disposed in the cavity C and mounted on the upper surface of the base board 201.
The base board 201 and the lid board 202 are formed of a glass board, for example, and through-holes 204 are formed in the base board 201 among both boards 201 and 202 so as to penetrate through the base board 201. In the through-holes 204, conductive members are buried so as to close the through-holes 204, thus forming penetration electrodes 205. The penetration electrodes 205 are electrically connected to outer electrodes 206 which are formed on the outer surface (lower surface) of the base board 201 and are also electrically connected to the piezoelectric vibrating reed 203 which is mounted in the cavity C. In addition, a bonding film 207 is formed over an entire surface of the lid board 202 facing the base board 201, and the bonding film 207 is anodically bonded to the base board 201.
Meanwhile, as shown in FIG. 23, in the course of manufacturing the piezoelectric vibrator 200, when the bonding film 207 and the base board 201 are anodically bonded, after setting the base board 201 and the lid board 202, which are superimposed onto each other, on an electrode base portion 208 for anodic bonding, a bonding voltage is applied between the bonding film 207 and the electrode base portion 208 while heating them to a bonding temperature. In this way, the bonding voltage is applied between the bonding film 207 and the electrode base portion 208 in a state where ions in the base board 201 heated to the bonding temperature have mobility, whereby current flows between the base board 201 and the bonding film 207. As a result, an electrochemical reaction can occur at an interface between the bonding film 207 and the base board 201, and both boards can be anodically bonded.
However, in the manufacturing method of the piezoelectric vibrator according to the related art, the anodic bonding is achieved in a state where the penetration electrodes 205 are in contact with the electrode base portion 208, and the piezoelectric vibrating reed 203 being electrically connected to the penetration electrodes 205 is adjacent to the bonding film 207. Therefore, there was a concern in that when the bonding voltage is applied between the bonding film 207 and the electrode base portion 208, a discharge phenomenon (spark discharge) may take place between the bonding film 207 and the piezoelectric vibrating reed 203.
Therefore, there was a problem in that when such a discharge phenomenon occurs, a sufficient amount of current does not flow between the base board 201 and the bonding film 207, and thus, the base board 201 and the bonding film 207 are not anodically bonded. In addition, if the discharge phenomenon takes place once, the bonding film 207 will be separated and scattered, and the scattered bonding film 207 will be stuck to the piezoelectric vibrating reed 203, for example, whereby a discharge path is formed between the bonding film 207 and the piezoelectric vibrating reed 203. Therefore, it is difficult to cause current necessary for the anodic bonding to flow between the base board 201 and the bonding film 207.